Raw material composition for soda-lime glass

ABSTRACT

The present invention provides a raw material composition for soda-lime glass capable of effectively suppressing formation of nickel sulfide (NiS) in the course of melting of the glass raw material. A nickel sulfide (NiS) impurity present in soda-lime glass is formed in a high-temperature vitrification step in which metal particles containing Ni and an Ni component of stainless steel used for the interior of a melting furnace, which are mixed into glass raw material, react at high temperature with a sulfur (S) component in Na 2 SO 4  serving as a glass raw material. However, when an additive containing an oxide, a chloride, a sulfate, or a nitrate of a metal is added in a very small amount and in advance to glass raw material, formation of NiS by the reaction between Ni and S in the course of melting can be suppressed or completely eliminated.

FIELD OF THE INVENTION

The present invention relates to a raw material composition forsoda-lime glass, and more particularly to a raw material composition forsoda-lime glass capable of effectively suppressing formation of nickelsulfide (NiS) in a glass base in the course of melting of the glass rawmaterial, to thereby produce a glass product of high quality.

BACKGROUND OF THE INVENTION

In a conventional method for producing soda-lime glass, in a step formelting glass raw material at a temperature as high as near 1,500° C. ina melting furnace, a nickel (Ni) component contained in stainless steelused for the interior of the melting furnace and Ni-containing metalparticles (e.g., stainless steel particles) present in glass rawmaterial as an impurity may be mixed into molten glass, and the Nicomponent may react with a sulfur (S) component in mirabilite (Na₂SO₄)serving as a glass raw material. As a result, nickel sulfide (NiS) maybe present as a fine impurity in a melt-molded glass substrate. Theincidence of an NiS impurity in a defective glass product is very low;i.e., the number of impurities is about one in some 10 tons (t) of glassproducts. In addition, the impurity has a spherical particle and theparticle size is as small as 0.3 mm or less, and thus detection of theimpurity in a production line is very difficult.

In order to process a substrate formed of such soda-lime glass intoglass for a building or a toughened glass plate for an automobile, thesubstrate is heated to the softening point (near 600° C.) and quenched,to thereby produce compressive stress in the surface layers of the glassplate.

When nickel sulfide (NiS) is contained as an impurity in toughened glasswhich is heated and cooled to ambient temperature in a toughening step,α-phase NiS, which is stable at about 350° C. or higher, is present inan unstable state. Since α-Phase NiS is unstable at ambient temperature,with passage of time it is transformed into β-phase NiS, which is stableat ambient temperature. The volume of NiS increases concomitant withphase transformation. A toughened glass plate contains a tensile stresslayer having a thickness which is about ⅔ the overall thickness of theplate, and thus cracks grow rapidly due to an increase in NiS volume inthe tensile stress layer, to thereby cause spontaneous breakage of theglass plate.

In order to prevent such spontaneous breakage of toughened glass, amethod for removing a defective product containing an NiS impurity isknown (which method is called soaking treatment). In the method,toughened glass which is heated and cooled to ambient temperature in atoughening step is placed in a firing furnace (a soaking furnace) andre-heated and maintained therein for a predetermined period of time, andany unstable α-phase NiS contained in the toughened glass is transformedinto β-phase NiS, which is stable at about 300° C. or less, to therebyincrease the volume of NiS and compulsorily break the defective glass.

However, in such steps mainly comprising thermal treatment, a longperiod time and a great amount of thermal energy are used in order toraise temperature, and thus production cost may increase. In addition,such steps raise a serious problem against reduction in production timeand enhancement of productivity.

SUMMARY OF THE INVENTION

In order to solve the aforementioned problems involved in conventionaltechniques, an object of the present invention is to provide a rawmaterial composition for soda-lime glass capable of effectivelysuppressing formation of nickel sulfide (NiS) in the course of meltingof the glass raw material.

Another object of the present invention is to provide a raw materialcomposition of soda-lime glass capable of effectively suppressingformation of NiS in the course of melting of the glass raw material whenthe material contains, as a coloring component, ferric oxide (Fe₂O₃),selenium (Se), cerium (Ce), or other metallic materials in a very smallamount.

DETAILED DESCRIPTION OF THE INVENTION

A nickel sulfide (NiS) impurity in soda-lime glass is formed in ahigh-temperature vitrification step in which metallic particlescontaining Ni and an Ni component contained in stainless steel used fora melting furnace, which are mixed into glass raw material, react with asulfur (S) component in Na₂SO₄ serving as a glass raw material. When anadditive including an oxide, chloride, sulfate, or a nitrate of a metalis added in a very small amount and in advance to glass raw material,formation of NiS by reaction between Ni and S in the course of meltingmay be suppressed or completely eliminated, for the reasons describedbelow. When a metal oxide is added in a very small amount to glass rawmaterial, NiS reacts with other metals to form a eutectic compound, andthe decomposition temperature decreases. When a chloride, sulfate, or anitrate of a metal is added in a very small amount to glass rawmaterial, oxidation is promoted, and thus formation of sulfides of Nibecomes difficult. As a result, formation of NiS may be suppressed.

In one embodiment of the present invention, the raw material compositionis characterized by comprising a mirabilite(Na₂SO₄)-containing glass rawmaterial to which an additive containing an oxide, a chloride, asulfate, or a nitrate of a metal is incorporated.

In another embodiment of the present invention, the raw materialcomposition is characterized by comprising a glass raw materialincluding mirabilite (Na₂SO₄) and, as a coloring component, at least onespecies selected from the group consisting of ferric oxide (Fe₂O₃),selenium (Se), cerium (Ce), and other metallic materials, wherein theglass raw material further include an additive containing an oxide, achloride, a sulfate, or a nitrate of a metal.

The aforementioned metal is at least one species selected from the groupconsisting of tin (Sn), iron (Fe), cobalt (Co), manganese (Mn), lead(Pb), lithium (Li), potassium (K), and sodium (Na). The percentage byweight of the aforementioned additives may be 0.15% or less on the basisof the total weight of the aforementioned glass raw material.

The incidence of an NiS impurity in a defective glass product is aboutone in some 10 tons (t) of glass products in a float-type meltingfurnace in practice, and the amount of Ni component contained in glassproducts is very low; i.e., 10 ppm (0.001 wt. %) or less. Therefore,only a ultra-very small amount of a metal oxide or the like is requiredto be added to glass raw material for the present invention to exhibitsufficient effects on reduction or complete elimination of formation ofnickel sulfide (NiS).

EXAMPLES Example 1

There was performed a test simulating the case in which nickel (Ni)metal reacts with a sulfur (S) component to thereby form nickel sulfide(NiS) in the course of melting of glass raw material in a float-typemelting furnace in practice.

The respective raw materials shown in Table 1 were mixed, to therebyprepare a glass raw material (200 g). Subsequently, powder of metallicNi (particle size: 149 μm) was added to the glass raw material in anamount by weight of 0.07% on the basis of the total weight of thematerial, to thereby prepare Ni-powder-containing glass raw material 1.

TABLE 1 Raw material Amount used (g) Silica sand 92.0 Soda ash 26.5Dolomite 23.6 Limestone 5.8 Mirabilite 2.0 Carbon 0.1 Cullet 50.0 Total200.0

Ni-powder-containing glass raw material 1 was placed in an aluminacrucible (volume: 250 cc), and the crucible was pre-heated at 600° C.for 30 minutes and placed in an electric furnace maintained at 1,370° C.The temperature was raised to 1,400° C. over 10 minutes. The cruciblewas maintained in the furnace at the temperature for 2.2 hours andremoved from the furnace. The thus-heated glass material was cast, tothereby prepare sample glass 1.

Table 2 shows the amount of added Ni powder (wt. %), the maximumparticle size of NiS particles (μm), and the number of NiS particles perglass weight (number/g) in sample glass 1. The number of NiS particleswas determined by observation under a stereoscopic microscope.

TABLE 2 Amount of addition Maximum particle Number (wt. %) size (μm)(number/g) Sample 1 0.0700 120 1.13

There were prepared five sets of glass raw material having the samecomposition as glass raw material 1 used for preparing sample glass 1 inwhich NiS was formed.

Tin oxide (SnO₂), an oxide of tin (Sn), was added to one of the abovefive sets of glass raw material, to thereby prepare glass raw materialcontaining Ni metal powder and SnO₂; i.e., glass raw material 2.

In the same manner, iron oxide (Fe₂O₃), an oxide of iron (Fe), was addedto one of the above five sets of glass raw material, to thereby prepareglass raw material containing Ni metal powder and Fe₂O₃; i.e., glass rawmaterial 3.

In the same manner, cobalt oxide (CoO), an oxide of cobalt (Co), wasadded to one of the above five sets of glass raw material, to therebyprepare glass raw material containing Ni metal powder and CoO; i.e.,glass raw material 4.

In the same manner, manganese oxide (MnO), an oxide of manganese (Mn),was added to one of the above five sets of glass raw material, tothereby prepare glass raw material containing Ni metal powder and MnO;i.e., glass raw material 5.

In the same manner, lead oxide (PbO), an oxide of lead (Pb), was addedto one of the above five sets of glass raw material, to thereby prepareglass raw material containing Ni metal powder and PbO; i.e., glass rawmaterial 6.

Each of these glass raw materials 2 to 6 was placed in an aluminacrucible, and the crucible was placed in an electric furnace, heated,and maintained in the furnace. Thereafter, the crucible was removed fromthe furnace. The thus-heated glass materials were cast, to therebyobtain sample glasses 2 to 6. Table 3 shows the amount of addedadditives (wt. %), the maximum particle size of NiS particles (μm), andthe number of NiS particles per glass weight (number/g) in therespective sample glasses.

TABLE 3 Amount of Maximum addition particle size Number Additive (wt. %)(μm) (number/g) Sample 2 SnO₂ 0.1500 200 0.52 Sample 3 Fe₂O₃ 0.1500 1200.50 Sample 4 CoO 0.1500 — 0.00 Sample 5 MnO 0.1500 200 0.47 Sample 6PbO 0.1500 200 0.67

As is apparent from Table 3, when a metal oxide is added in a very smallamount to the glass raw material, formation of NiS in a glass product iseffectively suppressed.

Example 2

There were prepared three sets of glass raw material having the samecomposition as glass raw material 1 used for preparing sample glass 1 inwhich NiS was formed.

Subsequently, sodium nitrate (NaNO₃), a nitrate of sodium (Na), wasadded to one of the above three sets of glass raw material, in an amountof 50% on the basis of the total amount of NaNO₃ and mirabilite (Na₂SO₄)in the glass raw material, to thereby prepare glass raw materialcontaining Ni metal powder and NaNO₃; i.e., glass raw material 7.

In the same manner, potassium nitrate (KNO₃), a nitrate of potassium(K), was added to one of the above three sets of glass raw material, inan amount of 50% on the basis of the total amount of KNO₃ and mirabilite(Na₂SO₄) in the glass raw material, to thereby prepare glass rawmaterial containing Ni metal powder and KNO₃; i.e., glass raw material8.

In the same manner, lithium nitrate (LiNO₃), a nitrate of lithium (Li),was added to one of the above three sets of glass raw material, in anamount of 50% on the basis of the total amount of LiNO₃ and mirabilite(Na₂SO₄) in the glass raw material, to thereby prepare glass rawmaterial containing Ni metal powder and LiNO₃; i.e., glass raw material9.

Each of these glass raw materials 7 to 9 was placed in an aluminacrucible, and the crucible was placed in an electric furnace, heated,and maintained in the furnace. Thereafter, the crucible was removed fromthe furnace. The thus-heated glass materials were cast, to therebyobtain sample glasses 7 to 9. Table 4 shows the addition condition ofmetal nitrates, the maximum particle size of NiS particles (μm), and thenumber of NiS particles per glass weight (number/g) in the respectivesample glasses.

TABLE 4 Maximum particle Number Addition condition size (μm) (number/g)Sample 7 NaNO₃:Na₂SO₄ = 1:1 300 0.25 Sample 8 KNO₃:Na₂SO₄ = 1:1 400 0.39Sample 9 LiNO₃:Na₂SO₄ = 1:1 300 0.20

As is apparent from Table 4, when a metal nitrate is added in a verysmall amount to the glass raw material, formation of NiS in a glassproduct is effectively suppressed.

Example 3

There were prepared seven sets of glass raw material having the samecomposition as glass raw material 1 used for producing sample glass 1 inwhich NiS was formed.

Iron (Fe) powder was added to one of the above seven sets of glass rawmaterial, to thereby prepare glass raw material containing Ni metalpowder and Fe; i.e., glass raw material 10.

In the same manner, iron oxide (Fe₂O₃), an oxide of Fe, was added to oneof the above seven sets of glass raw material, to thereby prepare glassraw material containing Ni metal powder and Fe₂O₃; i.e., glass rawmaterial 11.

In the same manner, iron chloride hydrate (FeCl₃.6H₂O), a chloride ofFe, was added to one of the above seven sets of glass raw material, tothereby prepare glass raw material containing Ni metal powder andFeCl₃.6H₂O; i.e., glass raw material 12.

In the same manner, iron sulfate hydrate (FeSO₄.7H₂O), a sulfate of Fe,was added to one of the above seven sets of glass raw material, tothereby prepare glass raw material containing Ni metal powder andFeSO₄.7H₂O; i.e., glass raw material 13.

In the same manner, iron nitrate hydrate (Fe(NO₃)₃.9H₂O), a nitrate ofFe, was added in different amounts (wt. %) to three of the above sevensets of glass raw material, to thereby prepare glass raw materialscontaining Ni metal powder and Fe(NO₃)₃.9H₂O; i.e., glass raw materials14 to 16.

Each of these glass raw materials 10 to 16 was placed in an aluminacrucible, and the crucible was placed in an electric furnace, heated,and maintained in the furnace. Thereafter, the crucible was removed fromthe furnace. The thus-heated glass materials were cast, to therebyobtain sample glasses 10 to 16.

Table 5 shows the additives, the amount of added additives (wt. %), themaximum particle size of NiS particles (μm), and the number of NiSparticles per glass weight (number/g) in the respective sample glasses.

TABLE 5 Amount of Maximum addition particle Number Additive (wt. %) size(μm) (number/g) Sample 10 Fe 0.1500 300 1.70 Sample 11 Fe₂O₃ 0.1500 1200.50 Sample 12 FeCl₃.6H₂O 0.1500 300 0.80 Sample 13 FeSO₄.7H₂O 0.1500120 0.73 Sample 14 Fe(NO₃)₃.9H₂O 0.1500 50 0.01 Sample 15 Fe(NO₃)₃.9H₂O0.1000 500 0.66 Sample 16 Fe(NO₃)₃.9H₂O 0.0750 137 1.03

As is apparent from Table 5, when an oxide, chloride, sulfate, ornitrate of Fe is added in a very small amount to the glass raw material,formation of NiS in a glass product is effectively suppressed.

In glass products actually produced in practice, the Ni content of glassis much lower than the value shown in Table 2; i.e., the content is 10ppm (0.001 wt. %) or less as described above, and therefore, the amountof the additive added to glass raw material is small. As is apparentfrom the results of the examples, even when the amount of additive is0.01 wt. % or less on the basis of the weight of glass raw material,sufficient effects may be obtained.

The above-described examples are applicable to glass raw material havinga composition including a coloring component; for example, ferric oxide(Fe₂O₃), selenium (Se), cerium (Ce), or other metallic materials in avery small amount.

Industrial Applicability

In the present invention, glass raw material comprises an additivecontaining an oxide, a chloride, a sulfate, or a nitrate of a metal in avery small amount, and thus formation of nickel sulfide (NiS) byreaction between nickel (Ni) and a sulfur (S) component in molten glasscan be suppressed. In addition, the amount of NiS in a glass product canbe greatly reduced.

Even when the aforementioned additives are added in very small amountsto a glass plate, physical properties of glass, including color,viscosity, and expansion coefficient, do not change, and the glass platecan maintain its original quality, which is very advantageous inpractice.

As described above, in the present invention, a glass product containingsubstantially no NiS can be produced. In practice, even when additivesare added in amounts of 0.01 wt. % or less to glass raw material, nickelsulfide (NiS) can be sufficiently reduced or eliminated. In addition,the production process for toughened glass does not require a soakingprocess, and thus production cost for the glass can be reduced.

Furthermore, soda-lime glass can be produced through a method similar toa conventionally-employed one, and thus conventional productionequipment can be used as is, and therefore it is not necessary to modifythe equipment or to build additional equipment. Therefore, quality oftoughened glass can be enhanced and equipment operating cost can bereduced.

What is claimed is:
 1. A raw material composition for soda-lime glass, comprising a mirabilite (Na₂SO₄)-containing glass raw material having the incorporation of an additive selected from the group consisting of a chloride of iron (Fe), Pb, or Li, a sulfate of Pb or Li, and a nitrate of Fe, Pb, or Li, wherein the additive suppresses formation of nickel sulfide in a resulting soda-lime glass.
 2. A raw material composition for soda-lime glass according to claim 1, wherein the percentage by weight of the additive is 0.15% on the basis of the total weight of the glass raw material.
 3. A raw material composition for soda-lime glass, comprising a mirabilite (Na₂SO₄)-containing glass raw material having the incorporation of lithium nitrate (LiNO₃), wherein about 50% of the amount of mirabilite (Na₂SO₄) contained in the glass raw material is replaced by the LiNO₃, wherein the LiNO₃ suppresses formation of nickel sulfide in a resulting soda-lime glass.
 4. A raw material composition for soda-lime glass, comprising a mirabilite (Na₂SO₄)-containing glass raw material having the incorporation of an additive selected from the group consisting of lithium nitrate (LiNO₃), Fe(NO₃)₃.9H₂O, and FeCl₃.6H₂O, wherein the additive suppresses formation of nickel sulfide in a resulting soda-lime glass.
 5. A raw material composition for soda-lime glass according to claim 1 or 3, further comprising at least one species selected from the group consisting of ferric oxide (Fe₂O₃) selenium (Se), and cerium (Ce), as a coloring component.
 6. A raw material composition for soda-lime glass according to claim 1, wherein the additive is a nitrate of Fe, the percentage by weight of the additive is from 0.075% to 0.15% on the basis of the total weight of the glass raw material, wherein the additive suppresses formation of nickel sulfide in a resulting soda-lime glass.
 7. A method of suppressing the formation of nickel sulfide during manufacturing soda-lime glass, comprising a step of reducing the formation of nickel sulfide by adding an additive selected from the group consisting of a chloride of Fe, Pb, or Li, a sulfate of Pb or Li, and a nitrate of Fe, Pb, or Li into a mirabilite (Na₂SO₄)-containing glass raw material.
 8. A method of suppressing the formation of nickel sulfide during manufacturing soda-lime glass, comprising a step of reducing the formation of nickel sulfide by adding an additive selected from the group consisting of LiNO₃, Fe(NO₃)₃.9H₂O, and FeCl₃.6H₂O into a mirabilite (Na₂SO₄)-containing glass raw material. 